Additional IP's... Routing vs Secondary on Vlan

Unanswered Question
Mar 13th, 2009
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We run a dedicated server business. \

We assign ONE VLAN per customer with a 8 IP subnet (5 Usable) for the primary IP of the server + 4 IP's the customer can use.

When assigning additional IP's to our dedicated server customers... which one of the following will take more processing power from the switch as traffic and more additional IP's are assigned to servers.

Method 1:

Adding another subnet of 8, 16 or 32 IP's to the SAME vlan that is assigned to the customer with a "Secondary" option like so

ip address secondary

to the same vlan of the customer


Method 2:

Doing a STATIC route to the Primary IP of the server (as the gateway) like so.

ip route (server's IP)

Which one in the long run as more and more additional IP's are assigned will take up more of the switch's resources.

Thank you very much for your input

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Richard Burts Fri, 03/13/2009 - 11:13
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I am not sure that either method would take more resources in the switch. With the secondary address, all of the addresses would be considered locally attached and therefore the switch would ARP for each address. Therefore you might say that the secondary approach would cause a somewhat larger ARP table. But I do not believe that this would be significant.

If you did the extra static route approach and if you were running a dynamic routing protocol then you would have to redistribute the static routes into the dynamic routing protocol. The redistributed routes would appear as external routes, which might or might not be something that you would want to consider.

From my perspective I might prefer to use the secondary address because it more clearly identifies the devices as members of the same VLAN. But from a resource consumption perspective I am not sure that there is much difference between them.




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